1. Field of the Invention
The present invention relates to rubber rollers for carrying media. More specifically, it relates to rubber rollers for carrying media, which have a high starting friction coefficient and a low degree of abrasion with little change in the friction coefficient even upon long-term use, as well as to an apparatus equipped therewith. The present invention also relates to an abrasion evaluation tester capable of evaluating the progress of abrasion without actually using the apparatus equipped with the rubber rollers. The present invention further relates to a method of selecting media with abrasion characteristics close to those of the actual medium to be carried.
2. Description of the Related Art
Rubber rollers are commonly used as means for carrying media such as normal copying paper and ink ribbons, printed pages, receipts, and the like. The characteristics required of rubber rollers for carrying such media are a high starting friction coefficient and little change in the friction coefficient even upon long-term use. These carrying properties are impaired when paper dust and dirt attach to the surface of the rubber rollers thus lowering the friction coefficient between the rubber rollers and the carried medium, or when ink on the surface of the carried medium attaches to the surface of the rubber rollers, thus lowering the friction coefficient and causing the carried medium to slip. Another cause is that as the rubber rollers are used, abrasion of the rubber leads to contour deformities, or the influence of the surrounding temperature and humidity, or oxygen and ozone causes the surface of the rubber rollers to become viscous, creating cracks and often making it impossible to carry the medium.
With recent information-related devices, more and more printing systems perform printing at a prescribed location, as in the case of printing on grid document sheets, printing on ruled line document sheets, printing on postcards, printing on bank deposit books, etc. In addition, laser printers connected to computer terminals require high-speed paper carrying and double-sided printing, while greater speeds for ejecting receipts of automatic cash dispensers at banks are also coming into demand. Abrasion resistant rubber is also desired for automatic ticket gate machines at train stations. Thus, rubber rollers with a rubber hardness of 60.degree. or less according to JIS-A are widely used to meet the demands of precise transport distance and speedy transport. As a result, replacement of the rubber rollers over smaller intervals of time becomes unavoidable because of their lower abrasion resistance and deformities in their dimensions with use. Abrasion is particularly considerable when employing carrying mechanisms which cause forced slipping between the rubber rollers and carried medium.
Materials widely used in rubber rollers for carrying media have conventionally included natural rubber, butadiene rubber, chloroprene rubber, urethane rubber, nitrile rubber, ethylene/propylene rubber, and the like, while silicone rubber and fluorine rubber are used in sections which require heat resistance. Most of these, with the exception of urethane rubber, have inferior abrasion resistance, and thus cannot withstand extended use especially in the case of mechanisms which carry media while forcefully causing slipping between the rubber rollers and the media, resulting in greater abrasion and shape deformity. Also, though urethane rubber has excellent abrasion resistance, paper powder from the medium and printing ink tend to attach to the surface of rubber rollers made therefrom resulting in a lower friction coefficient, and therefore slipping occurs with the carried medium and makes it impossible to perform the specified amount of carrying, or in the worst case causes total slippage and halts the carrying altogether. Thus, there presently do not exist rubber rollers capable of maintaining their original characteristics over long periods of use, and consequently rubber rollers must be periodically replaced.
A major reason complicating the development of rubber rollers whose carrying properties do not change over long periods of time is the fact that no convenient and suitable testers exist for the development of rubber rollers. Consequently, since most evaluations are performed with testers made to product specifications (hereunder, "actual device"), and long periods of time are required to evaluate whether the rubber rollers are able to withstand extended use, the types and numbers of rubber rollers which may be tested are limited. Furthermore, in tests which employ the actual devices, the unique characteristics of the actual devices themselves are exhibited, thus interfering with an objective evaluation. Consequently, there is need for the development of a tester with a carrying mechanism similar to that of the actual device, but which is capable of reproducing the same results of extended use of the actual device, and in a shorter period of time. Such an evaluating tester does not presently exist.
In addition, for the evaluation of the abrasiveness and change in the friction coefficient of rubber rollers which occur with the carrying of paper medium and the like, the evaluation tester must operate with the same carrying mechanism as the actual device, but it must also carry the same medium as the actual device. However, there are some cases in which the evaluating tester cannot carry the same paper as the paper used by the actual device. In such cases, it is necessary to select a medium which has a paper quality close to that of the paper medium and which is capable of being carried by the evaluating tester. The effect of the actual medium on the rubber roller is largely determined by the size of the friction coefficient and abrasive properties of the medium. Consequently, other types of carried medium may be used so long as the size of their friction coefficients and their abrasive properties are the same as those of the actual medium. Measuring devices employing strain gauges for the measurement of the sizes of friction coefficients are commercially available as products, but no methods are known for the evaluation of abrasive properties.